A passive device is referred to as a circuit device that is not capable of providing power gain. A capacitor, an inductor, and a resistor are all considered as passive devices for mainly filtering or blocking higher-frequency alternating current (AC). For example, a magnetic-core inductor that has a coil wound on a magnetic core may used as a choke or a common mode filter, and an assembly of a magnetic-core inductor and a capacitor that are electro-connected to each other may be used as an LC filter.
There are three types of commercially available inductors, namely thin film type inductors, multilayered type inductors, and wire wound type inductors.
TW patent application publication No. 201440090 A discloses a multilayered type inductor (see FIG. 1) and a method of making the same.
The method of making the multilayered type inductor includes the steps of: laminating a first circuit plate 110, a second circuit plate 120, a third circuit plate 130 and a fourth circuit plate 140 (see FIG. 2A); attaching an assembly of a supporting film 150 and a bonding pad circuit 160 to the first circuit plate 110 (see FIG. 2B); transferring the bonding pad circuit 160 from the supporting film 150 to the first circuit plate 110 (see FIG. 2C); removing the supporting film 150 from the bonding pad circuit 160 (see FIG. 2D); sintering the first, second, third and fourth circuit plates 110, 120, 130, 140 and the bonding pad circuit 160 so as to form a multilayered circuit substrate 100 (see FIG. 2E); and scribing the multilayered circuit substrate 100 using a scriber 170 (see FIG. 2F), so that the multilayered circuit substrate 100 can be broken into a plurality of multilayered type inductors 10 (see FIG. 1).
Referring to FIG. 1, each of the first, second, third and fourth circuit plates 110, 120, 130, 140 includes a respective one of non-magnetic bodies 111, 121, 131, 141 and a respective one of first, second, third and fourth circuit patterns 112, 122, 132, 142. Formation of the first, second, third and fourth circuit plates 110, 120, 130, 140 requires numerous steps (a total of at least 13 steps), including punching each non-magnetic body 111, 121, 131, 141 to form holes, filling the conductive paste in the holes, forming the first, second, third and fourth circuit patterns 112, 122, 132, 142 and sintering before laminating the first, second, third and fourth circuit plates 110, 120, 130, 140.
The conventional method may tend to cause undesired non-ohmic contact and Joule-heating generated at the interfaces between every two adjacent ones of the first, second, third and fourth circuit patterns 112, 122, 132, 142.
In order to prevent the undesired non-ohmic contact and Joule-heating and reduce the steps of the method of making the multilayered type inductor, TW patent No. 554355 discloses an improved chip inductor and a method of making the same.
Referring to FIGS. 3 and 4, the method of making the improved chip inductor includes the steps of: providing a ceramic substrate 200 which has a thickness of 150 μm; laminating on the ceramic substrate 200 a first circuit layer 210 with a predetermined pattern (such as a spiral coil), a first insulator layer 220 of polyimide (PI), a second circuit layer 230 with a predetermined pattern, a second insulator layer 240 of polyimide, and a third insulator layer 250 which is made from a PI-based material containing inorganic additives, such as Co, Fe, and Mn, so as to form a semi-product; heating the first and second circuit layers 210, 230 and the first, second and third insulator layers 220, 240, 250; forming a plurality of scribing lines (not shown) with a grid pattern on the third insulator layer 250 using a laser beam; and breaking the first and second circuit layers 210, 230 and the first, second and third insulator layers 220, 240, 250 along the scribing lines using a roller so as to form a plurality of chip inductors 2. The total thickness of the first circuit layer 210 and the first insulator layer 220 is 20 μm. The total thickness of the second circuit layer 230 and the second insulator layer 240 is 20 μm. The third insulator layer 250 has a thickness ranging from 20 μm to 30 μm.
Since the size of the aforesaid chip inductor 2 is 1 mm×0.5 mm or 0.6 mm×0.3 mm, it is too big to be used in a thin and small electronic device, such as a cellular phone.